In diesel-fueled engines, it is necessary to treat particles typically on the order of 0.1 micron in diameter. Each of the particles contains a solid, carbonaceous core with a soluble organic coating or shell of condensable hydrocarbon. Much of the hydrocarbon condenses on the core as the exhaust leaves the engine and the temperature drops.
The condensable hydrocarbon typically consists of relatively high molecular weight (heavy) hydrocarbon molecules in the range of C.sub.5 to C.sub.45, with correspondingly high boiling points, and condensable at about room temperature. Depending on the fuel and engine conditions, the condensable hydrocarbon comprises 20% to 80% of the mass of the particulate.
Diesel particulate can be collected and removed from an exhaust gas stream by various types of on-board filters or traps. These devices soon become clogged and must be cleaned or replaced. In order to remove collected particulate, the traps are heated by special heaters to temperatures greater than the exhaust temperature. This approach to treating particulate is technically difficult and costly, and introduces a variety of other problems. Accordingly, there is a need for an improved, relatively inexpensive method for treating diesel exhaust particulate to reduce the amount of particulate.